This invention relates to a fuel injection device, and more particularly to a fuel injection device of the electronic control type incorporated in an engine for a model (hereinafter referred to as "model engine").
A two-cycle or four-cycle glow engine which has been conventionally known to be a model engine includes a carburetor as indicated at reference numeral 100 in FIG. 6.
More particularly, the carburetor 100 includes a housing 101, in which a valve body 102 formed into a substantially cylindrical shape is arranged so as to be rotatable about an axis thereof. The housing 101 has upper and lower pipings 101a and 101b connected thereto so as to vertically extend therefrom, so that air is fed thereto through the upper piping 101a. Also, the valve body 102 is provided with a passage 102a in a manner to extend therethrough, which is arranged so as to communicate with the pipings 101a and 101b depending on a degree of opening of the valve body 102. The valve 102 has an operation arm 103 connected to a portion thereof projecting from one end of the housing 101. The operation arm 103 has an operation section of a servo mechanism (not shown) connected thereto in such a manner that the servo mechanism pivotally moves or rotates the vale body 102 in the housing. The valve 102 is provided with a needle 104 through screws, so that rotation of the needle 104 permits the amount of projection of the needle 104 into the valve body 102 to be adjusted.
The housing 101 has a needle valve 105 for fuel control or adjustment incorporated in the other end thereof. The needle valve 105 includes a pipe section 106 and a needle 107 arranged in the pipe section 106. The needle 107 is screwed to the pipe section 106 and provided on a proximal portion thereof with a lug 108, so that rotational operation of the lug 108 permits the needle 107 to be moved in an axial direction thereof in the pipe section 106, to thereby adjust a degree of opening of a distal end of the pipe section 106. The needle 104 in the valve body 102 is so arranged that a distal end thereof faces an opening formed at the distal end of the pipe section 106.
In the conventional carburetor 100 thus constructed, fuel fed to the needle valve 105 is injected into the valve 102 through a gap between the distal end of the pipe section 106 and the needle 107, to thereby be mixed with air fed into the valve 102 to prepare an air-fuel mixture, which is then fed to an engine. Operation of the lug of the needle valve 107 permits a flow rate of fuel to be adjusted, resulting in a flow rate of fuel or an air-fuel ratio sufficient to provide a maximum rotational speed of the engine being previously set. Operation of the valve body 102 by a servo mechanism adjusts the amount of air flowed into the valve body 102, so that the amount of fuel fed to the engine may be adjusted.
The conventional carburetor 100 fails to feed fuel in an amount corresponding to a large amount of air sucked into the valve body, to thereby unbalance an air-fuel ratio, when the engine is to be rapidly increased in rotational speed from a low level during idling or the like to a high level. Thus, the conventional carburetor 100 fails to smoothly or rapidly increase the engine speed and, in the worst case, stops the engine. Also, the carburetor fails to exhibit satisfactory responsibility, resulting in much time being required to change the engine speed from a lower level to a high level or from a high level to a low level. Also, when a model engine is mounted on, for example, a radio-controlled model airplane, centrifugal force generated during flight of the model airplane affects fuel fed to the carburetor, leading to a failure in appropriate feeding of fuel to the carburetor, resulting in satisfactory operation of the engine being impeded.
In view of such problems of the conventional carburetor, the inventors proposed a fuel injection device applied to a model engine. The fuel injection device proposed is constructed so as to inject, into a combustion chamber of a model engine, fuel electronically controlled and pressurized under a pressure corresponding to a pressure generated in a crank case of the model engine. The fuel injection device was expected to stably feed fuel to a model engine exposed to severe operational conditions while satisfactorily balancing an air-fuel ratio and ensuring good responsibility.
Unfortunately, it was found that the fuel injection device proposed by the inventors encounters some problems to be solved. More particularly, the fuel injection device is subject to restriction on a mounting position through which the device is mounted on the model engine. Also, it fails to be mounted directly in the combustion chamber of the engine to inject fuel directly into the combustion chamber. This is due to the fact that a pressure generated during compression and explosion strokes of the engine causes backflow of fuel to the fuel injection device and/or leads to a failure in sufficient compression of fuel in the fuel injection device.
Thus, the fuel injection device fails to pressurize fuel under a pressure generated in the crank case and therefore requires an additional fuel pressurizing unit specially designed, resulting in being increased in cost to a level excessive to or unsuitable for the model engine.
Also, in order to ensure increased combustion and output of the model engine by excessive feeding of fuel to the engine, the fuel injection device requires an excessive-feed tank and a pressurizing mechanism, to thereby be likewise increased in cost to a level excessive to the model engine.